The articles linked above and the comments here point out that the dependencies of a flutter app have to be considered as well.
So although the flutter license may be permissive enough other rights (patents, copyright, license of dependencies) may still pose a legal risk.

Do you have any additional information about "the licencse and right tree" of the dependencies?

Update 2

After the reply from user zimm i48 i would like to elaborate my question.

But what about the underlying involed compoents from dart / dart-sdk and other dependencies that are part of a flutter app?
– surfmuggleNov 21 '16 at 12:31

1

The license of the language something is written in doesn't really matter. Otherwise it would be impossible to write open source code using Visual Studio for example. Dependencies do matter, and the app's license should take them into account. If Flutter is BSD then all of its dependencies should be compatible with the BSD.
– curiousdanniiNov 21 '16 at 12:36

The script goes really deep. It literally unzips every last jar file, for example, even those nested inside other archives. It includes the license for things like the standard C library that we use, which is often forgotten by people writing license crawlers.

3rd party edit

Ian gave an answer at stackoverflow as well. Here is his content from over there:

There's an API you can use to find the list of licenses you need to show in your application.

For what it's worth, most of the code used by Flutter's engine is the same code as has previously been used by Chrome, Dart, and Android. The list is quite long mostly because the code is so mature that it has copyrights from many years and we have been advised to include each such copyright with a separate copy of the applicable license.

This sounds very interesting. It sounds like you did face the same problem that your company wanted to make sure that no "-poisonous-" / murky licenses are involved?
– surfmuggleNov 21 '16 at 19:21

Hey there Ian! It's great to see someone new around here! It would be great though if you could copy the information from your Stack Overflow answer here, so users don't have to navigate through a series of links. Aside from that though, welcome! :)
– Zizouz212♦Nov 24 '16 at 1:37

for those searching for it, AboutDrawerItem is now called AboutListTile
– Benoit JadinonMay 13 at 6:41

As noted by @curiousdannii, the license of the language itself does not matter. It is not considered a dependency. On the contrary, the standard library of the language could be a dependency. In that case, its license matters.

The license you've shown us for Flutter is a 3-clause BSD license. This is the kind of license most businesses will like because it does not impose many conditions. However, it does not contain a patent grant.

Even if the license did contain a patent grant (as with the Apache license), or if a patent grant came along, it would only grant you rights on patents filled by contributors of the software, not on patents possibly held by other people (who did not contribute).

Unless one can easily find patents which could be violated when using the software (as would be the case with audio/video codecs), or unless one has strong suspicions that the software developers hold patents which they are going to use against you if you use their FLOSS software (unlikely), the best strategy concerning patents is generally not to worry too much about them. There is no way you can be absolutely certain that by using a software you won't infringe on a patent so just use it until someone tells you to stop doing so.

The case of Facebook's ReactJS is a bit peculiar. The open source license cannot be revoked. But they have patents and they grant you a license for these as well. The latter license (patent grant) can be revoked if you sue them for infringing your patents. If your company does not hold any patents, you can use ReactJS without fear.

As can be seen here, Dart standard library is BSD3-licensed as well. But it apparently depends on some external libraries as well. Most probably these won't be part of your dependencies but you should make sure of that and check the license of any library you depend on.
– Zimm i48Nov 21 '16 at 17:23